Cut gem and article comprising such a gem

ABSTRACT

The invention relates to a cut gem comprising a girdle having four girdle sides and four girdle corners, a table realized by a flat facet, a crown which extends between the table and the girdle, in a first direction, and a pavilion which extends in a second direction, opposite to said first direction, between said girdle and a tip of the pavilion. The gem is noteworthy in that the crown has 24 facets, the pavilion has 32 facets and in that the four girdle sides are identical in the form of an arc of a circle, the concavity of which is oriented towards the outside of the gem.

The invention relates to cut gems and to articles comprising such gems.

In addition, it relates to improvements made to cut gems so that they have optical characteristics of light reflection that are superior to those obtained with a gem cut in the known “Princess” cut, so that the resulting brilliance is greater.

The Princess cut is widely used for gems, and is one of the cuts that gives the most brilliance to a diamond, just after the “round brilliant” cut.

U.S. Pat. No. 8,181,482 discloses a gem with a cut based on a Princess cut, reminiscent of a butterfly shape. The cut gem described in this document comprises:

-   -   a girdle having four girdle sides and four girdle vertices,     -   a table formed by a flat facet,     -   a crown which extends between the table and the girdle, in a         first direction,     -   and a pavilion extending in a second direction, opposite to said         first direction, between said girdle and a pavilion tip.

The invention aims to provide an alternative cut gem that is particularly brilliant.

For this purpose, it proposes a cut gem of the genre in question, which is noteworthy in that the crown has twenty-four facets, the pavilion has thirty-two facets, and the four girdle sides are identical in the form of an arc of a circle, of which the concavity is oriented towards the outside of the gem.

When cut in this manner, the gem has a more pronounced brilliance than that obtained with a gem as described in U.S. Pat. No. 8,181,482.

According to the invention, the gem may also have the features presented below, separately or in combination.

Concerning the crown, it may comprise:

-   -   four table corner facets, positioned at the four corners of the         table,     -   four sides, each of the four sides of the crown comprising:         -   at least one break facet,         -   a first crown star facet, positioned between the break facet             and a first table corner facet, and         -   a second crown star facet, positioned between the break             facet and a second table corner facet.

In the context of this embodiment, it may be arranged that the twenty-four facets of the crown comprise four lateral faces, four bezel facets, four break facets, eight star facets, and four table corner facets.

Moreover, according to an embodiment which will be presented below, a particularly high brilliance is obtained with a cut gem wherein:

-   -   the table lies in a table plane,     -   each bezel facet lies in a bezel plane,     -   and wherein the bezel plane is inclined relative to the table         plane at an angle substantially between 35 and 39°.

Concerning the pavilion, it may comprise:

-   -   four pavilion break facets,     -   a pavilion star having four pavilion star facets connecting the         pavilion tip and the girdle vertices, and     -   at least three lower pavilion facets positioned on each side of         each pavilion star facet, between a pavilion star facet and a         pavilion break facet among said four pavilion break facets.

In this embodiment, it may be provided that the thirty-two facets of the pavilion comprise four pavilion break facets, four pavilion star facets, and twenty-four lower pavilion facets.

Moreover, according to an embodiment which will be presented below, a particularly high brilliance is obtained with a cut gem wherein:

-   -   the table lies in a table plane,     -   each pavilion break facet lies in a pavilion break plane,     -   and wherein each pavilion break plane is inclined relative to         the table plane at an angle substantially between 58 and 62°.

To obtain even more brilliance, the cut gem may be created to have the following features:

-   -   each girdle side has a girdle side length which is the shortest         distance between two adjacent girdle vertices,     -   said pavilion star has a base of square cross-section near the         pavilion tip,     -   and the base of square cross-section has a diagonal whose length         is substantially between 5 and 11% of the girdle side length,         preferably between 5.5 and 10.5%.

The cut gem may also comprise the following characteristics:

-   -   each girdle side has a girdle side length which is the shortest         distance between two adjacent girdle vertices,     -   each girdle side has a maximum depth perpendicular to a line         connecting the two adjacent girdle vertices,     -   and said maximum depth substantially corresponds to between 5.5         and 9.5% of said girdle side length.

In addition, the cut gem may further comprise the following characteristics:

-   -   each girdle side has a girdle side length which is the shortest         distance between two adjacent girdle vertices,     -   the table has eight table vertices, of which four table vertices         are also table corners and the four other vertices, alternating         with the table corners, are also break facet vertices,     -   and the distance between a break facet vertex and the line         connecting the two adjacent girdle vertices, perpendicular to         said line, is substantially between 18 and 22% of said girdle         side length.

In accordance with one embodiment of the invention, the gem is a diamond.

The invention also relates to an article of jewelry comprising at least one gem as defined above.

In the following description, the invention is described in a sufficiently clear and comprehensive manner to enable its execution, accompanied by drawings in which:

FIG. 1 shows a gem according to an advantageous embodiment of the invention, in a top view,

FIG. 2 shows the gem represented in FIG. 1, in a bottom view,

and FIG. 3 shows the gem illustrated in FIGS. 1 and 2, in a side view.

In the following description, the terms “lower”, “upper”, “top”, “bottom” etc. are used in reference to the drawings to facilitate understanding. They are not to be understood as limitations to the scope of the invention.

The gem illustrated in FIGS. 1 to 3 is created starting with a diamond in a Princess cut (meaning a diamond whose general shape resembles a pyramid with a square base). However, it will be easy for a skilled person to perform the specific gem cut that will be described, on other precious or semi-precious stones.

In the following description, reference will first be made to an upper portion of the gem, meaning the portion of the gem that is usually presented to the exterior of an article of jewelry when the gem is set in jewelry. This is the portion of the gem that is directly visible to an observer.

In the conventional manner, the upper portion of the gem comprises a gem table formed by a flat facet and a crown surrounding the table and consisting of several adjacent facets. The crown extends substantially in a first direction H (see FIG. 3).

In contrast, the lower portion of the gem which is oriented towards the article of jewelry will be called the pavilion of the gem. The pavilion extends in a direction B that is opposite to direction H and will be described below in reference to FIG. 2.

FIG. 1 shows a top view of a gem according to the invention, and thus an upper portion of the gem, which has a general shape that is substantially square.

The “girdle” is the widest part of the gem, which gives its diameter: the gem shown in the figures thus has a girdle 3 that is substantially square in shape, with four vertices 1 (hereafter called girdle vertices) connected to each other by four girdle sides 2 each having the same length.

As can be seen in FIG. 1, each of the four girdle sides 2 is in the form of an arc (concave) of a circle, of which the concavity is oriented towards the outside of the gem.

FIG. 3 illustrates a girdle 3 side 2 of the gem, the girdle 3 being represented schematically with broken lines between the two girdle vertices 1 in FIG. 3.

At the center of the upper portion of the gem shown in FIG. 1, there is a table 4 of octagonal shape. Four of the vertices of the octagonal table 4 align with the girdle vertices 1 along a diagonal D1 or D2 of the girdle, and form the table corner vertices 5. The other vertices of the table 4 alternate with the table corner vertices 5 and constitute break facet vertices 6.

Each of the girdle 3 sides 2 has a girdle side length L, which is the shortest distance between two adjacent girdle vertices 1.

The break facet vertices 6 are each equidistant from the two adjacent girdle vertices 1. The position of a break facet vertex 6 is selected on a line D4, which is perpendicular to line D3 connecting the two girdle vertices 1 and which passes through the center C of the segment connecting the two girdle vertices 1. The distance L1 between the center C and the break facet vertex 6 is chosen so that it is substantially between 18 and 22% of the length L of the girdle side 2.

In the example illustrated in FIG. 1, the distance L1 between the center C and the break facet vertex 6 corresponds to substantially 20% of the length L between two girdle vertices 1.

The depth L2 of the concavities of the girdle sides 2 is also chosen according to the shortest length L between two girdle vertices 1 (see FIG. 1).

The depth L2 corresponds to substantially between 5.5 and 9.5% of the length L of a girdle side 2 (see FIG. 1).

The crown 7 of the gem is formed between the table 4 and the girdle 2 sides 2 (see FIGS. 1 and 3).

The crown 7 comprises, in the example illustrated in the figures, four lateral faces 8 which correspond to the four faces that follow the curvature of the girdle sides 2 (see FIG. 3).

At the four corners of the table 4, the crown 7 has four table corner facets 9 that are substantially diamond-shaped, of which one of the vertices is formed by a table corner vertex 5 and an opposite vertex is formed by a girdle vertex 1. The other two vertices of the table corner facets 9 are denoted T in FIG. 1.

The crown also comprises four bezel facets 10, formed by facets defined between two adjacent girdle vertices 1 and two vertices T of the two adjacent table corner facets 9 associated with the adjacent girdle vertices 1 and taken into consideration.

The incline of the bezel facets relative to the plane of the table 4 is such that the plane P1 of the bezel facets forms an angle α with the plane P2 in which the table 4 lies, the angle α being between 35 and 39° (substantially 37° in the example illustrated in FIG. 3).

The crown 7 further comprises four facets called break facets 11, triangular in shape, located between the bezel facets and the table 4, and having for vertices the two vertices 7 (in common with the bezel facets 10) and the break facet vertex 6 (in common with the table 4).

Finally, between the four table corner facets 9, the table 4, and the break facets 11, the crown has eight star facets 12 which are each triangular in shape, so called because they form a star around the table 4.

When cut in this manner, the gem according to the invention and shown in the figures comprises a crown 7 which has a total of twenty-four facets.

Reference will now be made to the pavilion of the gem according to the invention, with particular reference to FIG. 2.

The pavilion 13 extends between the girdle 3 and a pavilion tip 14 that it comprises. As the girdle 3 is substantially square in shape, the pavilion 13 has substantially the shape of a pyramid with a square base.

The pavilion 13 comprises a pavilion star 15 which has four arms connecting the pavilion tip 14 and each of the girdle vertices 1. The four arms of the pavilion star are called “pavilion star facets 16”.

Each of the arms has a wide base 17 and a narrow tip forming a point 18, which connects the girdle vertex. The wide bases 17 of the four pavilion star facets 16 form four abstract sides of a square (represented with dotted lines) of which the center is defined by the pavilion tip 14 (see FIG. 2).

In other words, near the pavilion tip 14, the pavilion star 15 has a base 19 of square cross-section.

According to one feature of a gem of the invention, the base 19 has a diagonal 20 whose length is between 5 and 11% of the girdle side length L, preferably between 5.5 and 10.5%. In this example, the length of the diagonal 20 is substantially equal to 8% of the length L.

In addition to the pavilion star 15, the pavilion 13 has four pavilion break facets 21 adjacent to the lateral faces 8.

Each pavilion break facet 21 is formed by a flat facet with three sides: the first side 22 is curved and is common with a side of the lateral face 8. The second and third sides 23 and 24 are of the same length and each of the second and third sides connects a girdle vertex 1 to a point 25 located on a line containing the diagonal 20.

The position of the point 25 on the line containing the diagonal 20 is determined by the orientation of a plane P3 of the pavilion break facet relative to the plane P2 of the table 4: according to the invention, the angle of incline β of plane P3 relative to plane P2 is substantially 60° (plus or minus 2°—see FIG. 3).

Between a pavilion break facet 21 and a pavilion star facet 16 are provided three lower pavilion facets 26.

Each lower pavilion facet 26 is triangular in shape, with a base 27 which is contained in the line containing the diagonal 20, and two sides connecting the base 27 to a girdle vertex 1.

The three lower pavilion facets 26 thus have three bases 27 aligned along the line containing the diagonal 20 and the point 25. Depending on the position of the lower pavilion facet 26, it may also have a side in common with a pavilion star facet 16 or with a pavilion break facet 21, or may have no such sides in common if the lower pavilion facet 26 is between two other lower pavilion facets 26.

In total, the pavilion 13 comprises twenty-four lower pavilion facets 26, where a base 27 is common to two lower pavilion facets 26 which are axially symmetric images of one another on an axis corresponding to the line containing the diagonal 20.

Thus implemented, the pavilion of the gem represented in the figures comprises thirty-two facets including twenty-four lower pavilion facets 26, four pavilion break facets 21, and four pavilion star facets 16.

The invention is not limited to the specific gem just described. Furthermore, the invention extends to any article of jewelry comprising at least one gem such as the one described and represented above. 

1. A cut gem comprising: a girdle having four girdle sides and four girdle vertices, a table formed by a flat facet, a crown which extends between the table and the girdle, in a first direction, and a pavilion extending in a second direction, opposite to said first direction, between said girdle and a pavilion tip, wherein the crown has twenty-four facets, the pavilion has thirty-two facets, and the four girdle sides are identical in the form of an arc of a circle, of which the concavity is oriented towards the outside of the gem.
 2. The cut gem according to claim 1, wherein said crown comprises: four table corner facets positioned at the four corners of the table, four sides, each of the four sides of the crown comprising: at least one break facet, a first crown star facet positioned between the break facet and a first table corner facet, and a second crown star facet positioned between the break facet and a second table corner facet.
 3. The cut gem according to claim 2, wherein the twenty-four facets of the crown comprise four lateral faces, four bezel facets, four break facets, eight star facets, and four table corner facets.
 4. The cut gem according to claim 3, wherein: the table lies in a table plane, each bezel facet lies in a bezel plane, and wherein a bezel plane is inclined relative to the table plane at an angle substantially between 35 and 39°.
 5. The gem according to claim 1, wherein said pavilion comprises: four pavilion break facets, a pavilion star having four pavilion star facets connecting the pavilion tip and the girdle vertices, and at least three lower pavilion facets positioned on each side of each pavilion star facet, between a pavilion star facet and a pavilion break facet among said four break facets.
 6. The cut gem according to claim 5, wherein the thirty-two facets of the pavilion comprise four pavilion break facets, four pavilion star facets, and twenty-four lower pavilion facets.
 7. The cut gem according to claim 5, wherein: the table lies in a table plane, each pavilion break facet lies in a pavilion break plane and wherein each pavilion break plane is inclined relative to the table plane at an angle substantially between 58 and 62°.
 8. The cut gem according to claim 5, wherein: each girdle side has a girdle side length (L) which is the shortest distance between two adjacent girdle vertices, said pavilion star has a base of square cross-section near the pavilion tip, and wherein the base of square cross-section has a diagonal whose length is substantially between 5 and 11% of the girdle side length.
 9. The cut gem according to claim 1, wherein: each girdle side has a girdle side length which is the shortest distance between two adjacent girdle vertices, each girdle side has a maximum depth perpendicular to a line connecting the two adjacent girdle vertices, and wherein said maximum depth substantially corresponds to between 5.5 and 9.5% of said girdle side length.
 10. The cut gem according to claim 1, wherein: each girdle side has a girdle side length which is the shortest distance between two adjacent girdle vertices, the table has eight table vertices, of which four table vertices are also table corners and the four other vertices, alternating with the table corners, are also break facet vertices, and wherein the distance between a break facet vertex and the line connecting the two adjacent girdle vertices, perpendicular to said line, is substantially between 18 and 22% of said girdle side length.
 11. The ccut gem according to claim 1, wherein the gem is a diamond.
 12. The article of jewelry comprising at least one gem according to claim
 1. 